Polypropylene is known in the art as a suitable material from which to manufacture transparent containers. Conventionally, an extrusion blow-molding process has been used, but such a process, although capable of producing integral handles, results in bottles with low clarity and impact strength.
U.S. Pat. No. 6,733,716, issued on May 11, 2004, discloses a process of stretching a polyethylene terephthalate (PET) preform with a stretch rod; blowing the preform into the shape of a bottle in the mold; discharging blow gas from the stretch rod onto an interior wall surface where the handle is to be formed; and advancing movable mold segments within the blow-mold from a first retracted position to a second position thereby compressing an interior wall surface of the article into contact with a facing interior wall surface of the bottle to bond the surfaces at an elevated temperature and form an integral handle extending from the exterior wall of the blow-molded article.
However, this prior art process of completing the pre-blow to form the container shape before utilising the moving mold segments will result in either extensive material over-stretching at the handle area, or require the use of significantly thicker-walled preforms, and resulting bottles, than is optimum. In addition, due to the surface characteristics of PET and the difference between its melt and blow temperature, PET is not suited to bonding to itself. Therefore, trimming off the bonded section whilst retaining liquid-tightness at the handle becomes unfeasible.
The need remains for an economical process for the manufacture of a transparent container which comprises an integral handle.